Last year, the US president, Barack Obama, acknowledged that Lo Porto and an American named Warren Weinstein, 73, had accidentally been killed in a secret counter-terrorism mission and expressed his regret for the deaths.

The payment was confirmed by the US embassy in Rome and Lo Porto’s brother, Daniele. Details of the agreement were first reported by the Italian newspaper La Repubblica.

A spokesperson for the US embassy in Rome said the government had confirmed at the time the deaths were announced that it would be providing a condolence payment to both families.

“We did that knowing that no dollar figure would ever bring back their loved ones and, out of respect for the families, we are not sharing any details of those payments,” they said.

It is not clear whether the Weinstein family has also received a payment.

Experts say it is already understood that the US offers condolence payments to the families of civilian casualties of airstrikes in and Iraq, but that the Lo Porto agreement stands out because he was killed in Pakistan and because documents show the US was directly involved in the payment.

In Yemen, , whose nephew and brother-in-law were killed in a 2012 drone strike, received a cash payment of $100,000 from a Yemeni official, and no acknowledgement or apology from the US.

The agreement between the US government and the Lo Porto family was signed on 8 July, according to documents obtained by La Repubblica that were shared with the Guardian. The payment – €1,185,000 in total – was considered a “donation in the memory of Giovanni Lo Porto”.

The agreement was signed by a diplomat named Garrett Stephen Wayne, in his role as financial management centre director of the US embassy in Rome. The agreement clarified that Lo Porto was killed in Pakistan. The White House acknowledged at the time of the announcement that he was killed in the border region between Afghanistan and . The payment was made to Lo Porto’s mother, Giusy, who lives in Palermo, and his father, Vito.

The agreement includes this stipulation: “This does not imply the consent by the United States of America to the exercise of the jurisdiction of the Italian courts in disputes, if any, directly or indirectly connected with this instrument. Nothing in this instrument implies a waiver to sovereign or personal immunity.”

Jack Serle, an expert on the drone programme and journalist at the Bureau of Investigative Journalism, said it was the first time he had heard of such a payment that had demonstrably come from the US Treasury.

“It has been a common tool in Afghanistan and Iraq. It is not accepting responsibility, but is used to try to soothe the anger, essentially saying sorry for the event and for what happened, while also not accepting responsibility,” Serle said.

People who study the issue said it was far from clear whether the development signified a shift in policy in favour of the families of victims.

“I don’t know what kind of impact this will have on all the other people who think they may have claims because nominally those strikes remain unavowed,” Serle said.

Jennifer Gibson, from the human rights group Reprieve, said payments were not a substitute for genuine transparency.

“I think at this point there is no indication that this goes beyond the compensation of a western hostage killed in a drone strike,” Gibson said. “The Lo Porto and Weinstein families are the only families that have been acknowledged and apologised to by the administration. Thus far there hasn’t been a single Pakistani or Yemeni family that has received the same acknowledgment.”

In a statement, Lo Porto’s mother expressed her sorrow about his death: “I will not see my son at home with his smile. They took my precious son and they also killed me. Now all that remains for me is to wait until the last day of my life for divine, not earthly, justice.”

last April, four months after the drone strike in January against an al-Qaida compound. The admission was made only days after the Italian prime minister, Matteo Renzi, visited the White House.

Barack Obama makes a statement about the death of the two hostages at the White House in April 2015. Photograph: EPA

The US government announced in July that drone and other airstrikes have killed between 64 and 116 civilians during Obama’s administration, a tally that was criticised as too low by some experts.

Between 2009 and 31 December 2015, the administration claimed that it launched 473 strikes, mostly with drones, that killed between 2,372 and 2,581 terrorist “combatants”.

A report in the Washington Post last year said the “” as part of an internal investigation into the killing of Weinstein. Citing US officials, the report said footage examined before the lethal drone strike showed a possible hostage in the area.

, Daniele Lo Porto said his family felt abandoned by Italian and US officials, who never got in touch again after the initial round of public condolences.

It is unclear why the US agreed to make the payment in July and the embassy declined to provide any further details about the transaction.